Tube device



Patented Dec. 24, 1929 UNITED STATES PATENT OFFICE LEE SUTHERLIN .AND HUBERT M. FREEMAN, OF EAST PITTSBURGH, PENNSYLVANIA,

ASSIGNORS TO WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A COR- PORATION OF PENNSYLVANIA TUBE DEVICE Application filed February a, "1923.. serial No. 617,876.

2 Our invention relates to vacuum-tube devices having particular relation to methods of degasifying such devices. In its broad aspect, the principal object of our invention 5 is to provide an improved method of treat- 1 the overheating of the elements at any time during the exhaust treatment; by a greater uniformity in operating characteristics obtainable during quantity-production methods of manufacture than has heretofore been possible; and by the material economies effected in the time necessary for the evacuation treatment, the last-mentioned characteristic being of particular importance inasmuch as the value of the operators time is commensurate with'that of the materials constituting the tube.

More specifically, another object of our invention is to provide a'reagent or so-called getter whichoperates continuously to clean 5 up such gases as are evolved during the normal operation of the tube, i. e., to maintain the tube continuously in a hard condition.

In the ordinary methods of evacuating tube devices prior to our invention, it has been customary to bake the tube structures and then to further heat the same by an induction furnace or by electron bombardment, all the while subjecting the tube to an exhaust treatment to remove the gases contained therein. The tube was next sealed from the exhausting system and the residual gases remaining within the device were cleaned up by the volatilization of certain reagents, whereupon the evacuation process of the tube was considered to be complete. According to such prior art methods of evacuating or hardening tubes by means of getters, it was absolutely essential to vaporize the getter material, the clean-up action occurring dur- 4.5 ing the period of vaporization, as shown, for

instance, in the patent to Frederick Soddy T No. 859,021, granted July 2, 1907. for means and apparatus for producing high vacuums. After considerable experimental work, we

I have found that the lengthy evacuating process of the prior art, involving the volatilizat1on of certain clean-up agents or so-calledgetters, may be entirely avoided by an evacuating process wherein the clean-up agent is inserted in the tube and the whole then baked fora period of time to remove the water and the occluded gases therefrom all the while decreasing the pressure within said tube; When the tube has been pumped as hard as is practically possible, it is sealed and thereafter the residual gases remaining or formed within the tube are removed by the action of the clean-up .agent.

We have found that the rate of clean-up of the residual gases after the sealing of the tube is very materially increased by subjecting the same to an-electrical treatment, as, for example, energization of the cathode and anode elements thereof to establish an electronic discharge therebetween.

Other objects and applications of our invention, as well as details of construction and operation thereof, will be apparent from the following description and claim and the accompanying drawing, wherein:

Fig. 1, is a view, partially diagrammatic and partially structural, showing one form of apparatus for carrying our process into effect, together with certain necessary electrical circuits.

Fig. 2 is a detail View of a vacuum-tube structure at one stage in the development thereof illustratin particularly, one method of including the cean-up agent or so-called getter within the completed tube shown in Fig. 1.

Fig. 3 is a detail View of the vacuum tube structure illustrating, particularly, the bulb portion of the tube prior to the welding thereof to the structure of Fig. 2.

In Fig. 1 is shown a vacuum-tube device 1 of any well-known design comprising a containing envelope or tube 2 having an anode 3, a grid 4 and a hot cathode 5 suitably supported therein from a press .6 which forms the terminus of a re-entrant tube portion 7. The anode, grid and cathode elements 3, 4 and 5 are respectively provided with external terminal connections 8, 9 and 10, 11, the cathode ,terminal'connections 10, 11 being connected to asource 12 of direct-current energy through a resistor 13 and a disconnecting switch 14", the anode and cathode terminal connections 8 and 11 being connected to a high-potential energy source 15 and a discon necting switch 16, all as explained more fully hereinafter.

A clean-up agent or so-called getter 17 ,com-. prising preferably lime is shown applied to the press 6 in the form of a coating, although, of course, it may be positioned in any other portion of the tube 2 not subject to high temperatures and in other forms than a coating. I

A main exhaust pipe 18, which is connected to the envelope 2' by means of a tip 19, is sealed to a vacuurnpump (not shown) having a capacity suflicient to reduce the pressure within the envelope 2 to a very low value.

The vacuum-tube device 1 may be subjected to heating energy tending to drive off the watervapor and other occluded gases therein by positioning the same in an oven 20 which is shown in longitudinal section. The oven 20 may be heated in any well know'n manner and, in order to simplify the description of our invention, the heating means is not shown."

By way of illustration, we shall now describe an exact process which has proved satisfactory in practice, though it is to be expressly understood that our invention, in its' broader aspects, is not strictly limited to the precise details and features hereinafter set forth. Experimentation has shown that a number of materials will operate as getters to some extent when employed in the process constituting our invention, as for instance,

barium hydroxide, or sulphur, but we found that calcium oxide results.

The calcium oxide or so-called lime constituting the getter, is preferably prepared gives the'best all-around in such way as to have a spongy texture, that is, one filled with a large number of minute pores, as is found in lime prepared from limestone. The lime, which is obtained from such sources as just described, is mixed with distilled water and thereby hydrated to make a thin paste containing calcium hydroxide which is then applied to the press 6 of the vacuum tube at the stage of development in the manufacture thereof shown in Fig. 2.

The structure of Fig. 2 is then inserted within the bulb shown in Fig. 3 and the lower end of the bulb is welded to the entrant tubeportion 7 to produce the vacuum-tube structure shown in Fig. 1, the latter having a single external opening or tip portion 18 only.

The tube structure is then placed within the oven 20 and the tip sealed to the main exhaust tube 18. The temperature within the oven 20 is now raised to approximately 100 C. and maintained for 10 or 15 minutes until the water vapor and occluded gases within the materials of the tube device have been driven off, the same being removed all the-while through the main exhaust tube 18. During thisitreatment it is thought that the "calcium hydroxideisreduced to calcium oxide by evolution of the contained and combined water which calcium oxide is very active, both chemicall and physically, easilyforming ,compoun s with water vapor and carbon dioxide, and physically adsorbing the gases with which itis non-reactive such as hydrogen, oxygen, nitrogen, and the rare gases,

the gasesmost likely toremain in-the'tube afterthe exhaust treatment just mentioned.

The vacuum-tube device is now sealed off from the main exhaust tube 18 and the tube is subjected to an aging treatment to increase the rate of clean-up efi'ectedby the getter 17 which is disposed on the press 6 of the tube 2. The aging treatment just mentioned comprises theestablishment of a. current of approximately normal valuein the filament 5- by closing switch 14 and the establishment'of an electron stream therein by the application of a plate-filament voltage also of approximately normal value by closing switch 16. For the particular tube experimented upon, the filament current was .3 of an ampere and the plate potential 100 volts but it was observed that the-rate of clean-up could be materially increased'by exceeding these values. The length of time necessary for the aging depends entirely upon the degree of evacuation of the tubes subsequent to the pumping'operation, so that the aging may range from 'a few seconds to an hour or more. g

The phenomena obtaining withinthe tube 2 when the getter .19 is functioning as a cleanup agent are not very well understood but it is thought thatpossibly the cleaneup action of the residual gases is partly the result of the formation of stable chemical compounds with the active getter material as well as partly by an adsorption of the gases by. the finely divided porous material-of-the getter, although, of conrse,'it is to be expressly understood that tain it in an extremely high state of evacuak first treated as hereinbefore described to remove all-gases whereupon the desired gas or vapor is added until the getter ceases to function and the inside pressure of the tube device remains at the desired operating value.

"In suinmary, we'desire again to emphasize the fact that, inour method of evacuatiomthe operation of the getter 17 is not the result of the volatilization of the same, inasmuch as the getter 17 at no time during the manufacture or subsequent operation of the tube is subjected to such heat as would cause volatilization. Our invention, therefore, differs radically from prior getter-s requiring volatilization.

While We have shown and described a particular embodiment of our invention and vwhile we have specified certain specific values in connection therewith, for the purpose of more fully describing and illustrating the principles of the invention, it is apparent that various changes and modifications may be made therein without departing from the spirit and scope thereof. \Ve desire, therefore, that only such limitations shall be im- 

